Partial purification and characterization of an alkaline serine protease produced by Streptomyces griseus NCRRT and its antifungal effect on Fusarium solani.

The antifungal activity of different actinomycetal isolates was tested, in vitro, against the soil-borne plant pathogen, Fusarium solani, grown on PDA medium. Among the tested isolates, Streptomyces griseus (accession number AB723782) showed the highest growth inhibition against the tested fungus and this was principally due to a proteolytic activity. The alkaline protease produced by this strain, was partially purified by ammonium sulphate precipitation, then was subjected to a sephacryl S-300 gel filtration column chromatography. These treatments afforded 2.15-fold increase in the specific activity of the crude enzyme, a 3.5 % recovery and an about 7.5 purification fold. The enzyme exhibited the highest activity at pH 8 and 55°C. Stability studies showed that, after 30 minutes of preincubating the enzyme at pH range of 6 to 10, it retained more than 80% of its original activity. Also, after 60 minutes of preincubation at temperature range from 25 to 50°C, it retained 70% of its original activity. Moreover, phenyl methyl sulphonyl fluoride (PMSF) strongly inhibited the enzyme activity suggesting that it is a serine protease enzyme. The K and V values exhibited m max by the partially purified protease at the optimum conditions were 2.5 mg/ml and 190 U/mg protein, respectively, using casein as substrate. The partially purified enzyme was found to inhibit the growth of F. solani less than the crude filtrate, indicating that the mode of action of this enzyme takes place through a synergistic relationship with other lytic enzymes.